In recent years, in order to prevent information leakage from computer terminal devices, to facilitate management of applications on the terminal side, and the like, a thin client system has come to be introduced, in which all applications to be input/output by and displayed on terminal devices are executed by a server device and all generated files, accompanying thereto, are also managed in the server device.
In such a thin client system, drawing data of an application program executed by a server device is transferred to a terminal device on the client side over a network such as LAN, and is displayed on a screen of the terminal device. As such, if the processing amount of drawing data increases or if the number of terminal devices to be connected with the server device increases, the load placed on the server device for transferring the drawing data to the terminal devices increases, which causes problems such as degradation in response time and a significant limitation to the number of connecting terminal devices.
As such, as a technology to control displaying of drawing data by software, it has been considered to clip only a rectangle drawing region including a drawing data portion in which the drawing is updated within one screen, and further, compress it as required and transmits it, to thereby reduce the amount of data involved in transfer of the drawing data of the computer screen so as to reduce the load placed on the server device.
Various methods have been proposed to detect an update region. For example, Patent Document 1 discloses a method of dividing a screen into blocks, and transferring only blocks including pixel differences. Further, in Patent Document 2, “background art” section, for example, describes a method of transferring an image included in a smallest rectangular region including all regions in which differential values from the previous frame are detected.
Further, in Patent Document 2, “best mode for carrying out the invention” section, for example, describes an update region detection method as described below. First, a screen is divided into blocks, and for each block, the smallest rectangular region, including all regions in which differential values from the previous frame are detected, is detected. Next, if both blocks adjacent to each other horizontally or laterally include the rectangular regions and the rectangular regions are in contact with each other horizontally or laterally, a smallest rectangular region including both rectangular regions of the blocks adjacent to each other horizontally or laterally are used as an update region.
On the other hand, Patent Document 3 discloses a method of dividing a right-angled polygon area, generated on a layout surface of an integrated circuit by a floor plan, into a plurality of rectangular regions. Further, Patent Document 4 discloses a method of detecting a rectangle having the largest area within one region, from among a plurality of regions present in an image. However, Patent Documents 3 and 4 fail to suggest applying the technologies to processing of detecting an update region from previous and subsequent frames of drawing data. Further, Patent Documents 1 and 2 do not contain description suggesting dividing a region into a plurality of rectangular regions when detecting an update region from previous and subsequent frames of drawing data, and detecting a rectangle having the largest area within one region.
Patent Document 1: JP 2009-017414 A
Patent Document 2: JP 2005-033763 A
Patent Document 3: JP 2000-020566 A
Patent Document 4: JP 2007-140593 A